Potassium nitrate, KNO3, is an industrially important chemical with a variety of uses from fertilizers to explosives. It is primarily obtained either by mining of KNO3 deposits or by methods that ultimately derive from nitrogen fixation via the Haber process.
Methods for production of KNO3 from syngenite (K2Ca(SO4)2) are known in the literature. For example, Canadian Pat. No. 1217027 to Worthington et al. and German patent 3525654 to Löblich et al. disclose methods for producing KNO3 from syngenite via reaction with CaNO3.4H2O.
Polyhalite, Ca2MgK2(SO4)4.2H2O, is widely distributed and readily available potassium-containing mineral. It has been known for some eight decades (see, for example, Partridge, E. P. Ind Eng. Chem. 1932, 24, 895) that polyhalite can be a useful starting material for production of potash and potassium sulfate. Commercially viable methods that use polyhalite as a starting material for formation of KNO3 remain as yet unknown, however. A more efficient means for converting raw polyhalite into salts such as potassium nitrate, while increasing the quantity of gypsum relative to that in the raw polyhalite and controlling the relative quantity of KNO3 and potassium magnesium sulfates produced from the polyhalite, remains a long-felt need.